1. Field of the Invention
The present invention relates to a spindle motor having an aligning mechanism for disk-shaped recording media including, for instance, minidisks (MDs), CDs and DVDs, and an information recording/reproducing apparatus mounted with such a spindle motor.
2. Related Background Art
Conventionally, alignment of an optical disk-shaped recording medium with the rotation shaft of an information recording/reproducing apparatus is accomplished with an aligning member provided on a spindle motor for turning the optical disk-shaped recording medium. To illustrate it in more specific terms, a spindle motor mounted on a disk drive for MDs or the like is shown in FIG. 5. Incidentally, this example of conventional aligning structure is substantially the same as an aligning structure of the invention disclosed in the Japanese Patent Application Laid-Open No. 2003-36585.
A spindle motor 30 is configured of a stator unit 31 disposed stationarily and a rotor unit 32 supported to be turnable relative to the stator unit 31.
The stator unit 31 comprises a stator board 33, a housing 34 fitted to the stator board 33, wound coils 35 stationarily disposed to surround the housing 34 from outside, and a plain bearing 36 held within the housing 34 by pressure fitting or otherwise. On the other hand, the rotor unit 32 comprises a rotation shaft 8 turnably held by the plain bearing 36, a turntable 5 fitted to this rotation shaft 8, a cylindrical rotor yoke 9 with an open lower end fitted to this turntable 5 and surrounding the wound coils 35 from outside, a rotor magnet 10 provided within this rotor yoke 9, an attracting magnet 41 disposed on the upper face of the turntable 5, an aligning member 3 slidably fitted into a turntable cylinder portion 6, a restrictive member 43 for restricting the upward movement of the aligning member 3, and a force-applying member 44 for applying an upward force to the aligning member 3 relative to the turntable 5.
Further a disk 1 having an attractable plate 46 over the center hole is mounted on the turntable 5 and, by attracting the attractable plate 46 with the magnetic attraction of the attracting magnet 41 of the rotor unit 32, the disk 1 is mounted on the turntable 5. In this mounting process, the center hole lower end 2 of the disk 1 comes into contact with a tapered face 4, which is the contact portion of the aligning member 3, the aligning member 3 is pressed downward against the force of the force-applying member 44, and the disk 1, aligned to be substantially coaxial with the rotation shaft 8, is mounted on the turntable 5. Incidentally, the force-applying member 44 is disposed to compensate for any tolerance fluctuation of the center hole bore of the disk 1. In other words, the fixation of the aligning member 3 makes impossible compliance with tolerance fluctuations of the center hole bore of the disk 1. When the center hole bore is at its minimum, the disk 1 cannot be mounted on the turntable 5, or when the center hole bore is at its maximum, the backlash from the aligning member 3 increases, making alignment impossible. Additional in this conventional arrangement, the force-applying member 44 uses a compressive coils spring having a round section to prevent the coils from being deformed by compression.
The conventional spindle motor 30 is configured as described above, wherein the rotor unit 32 is rotationally driven by a magnetic field generated on the wound coils 35 by appropriately supplying electricity to the wound coils 35, and the rotor magnet 10 of the rotor unit 32 and the magnetic field derived from the rotor yoke 9 act on each other. In synchronism with the rotation of the rotor unit 32, the disk 1 mounted on the turntable 5 is enabled to turn without slipping by the attractive force of the attracting magnet 41.
When information is to be recorded onto or reproduced out of the disk-shaped recording medium (hereinafter referred to as simply “disk”), it is necessary to accurately align the track position on the disk and the position of the pickup for recording/reproducing information. Especially if the disk becomes eccentric, the track position will vary in the radial direction of the disk in each turn of the disk correspondingly to the extent of eccentricity. For instance where a CD is played back, pit signals of 1.6 μm in pitch are accurately traced to detect the recorded signals. To accurately align this pickup position, alignment in the radial direction of the disk is accomplished according to the prior art by tracking servo, for instance.
However, in recent information recording/reproducing apparatuses, the disk is turned increasingly faster along with the narrowing of the track pitch and the rise of the transfer rate to meet the need of increased density of information. As a result, the alignment of tracking servo is required to be more accurate and faster. However, it is evidently difficult to achieve more accurate and faster control while maintaining the operating range of tracking servo as it is, and the range tends to be narrowed, making it indispensable to reduce eccentricity.
For this reason, the currently used method is, as described above, to configure an aligning member having a tapered face, which fits with the guide portion of a turntable to be mounted with a disk and comes into contact with the center hole of the disk to be slidable in the direction of the rotation axis of the turntable, and thereby to absorb any tolerance fluctuation of the center hole of the disk to achieve highly precise alignment. However, this involves a problem that the play needed for this sliding causes the aligning member to incline and accordingly to vary the angle of the taper face, inviting eccentricity at the time of mounting the disk. This problem is usually addressed by fabricating the turntable and the aligning member together constituting the play for sliding from metallic materials which permit precision machining so as to minimize the play for sliding. However, by reason of the limitation of machining accuracy, it is also necessary to allow for a tolerance fluctuation of 5 to 10 μm to the diameter of the guide portion disposed on the turntable and the sliding portion of the aligning member, which together constitute the play for sliding. Therefore, even if the tolerance fluctuation due to the combination of the guide portion and the sliding portion is minimized to 0 μm (though sliding is virtually impossible with a play of 0 μm between the sliding portions), the play can be as large as 20 μm at the maximum depending on the combination, which would cause the aligning member to substantially incline, resulting in increased eccentricity. For this reason, by the conventional process, even if the aligning member and the turntable are cut from metallic materials permitting precision machining, the constituent parts should go through screening by dimensional inspection to reduce the tolerance fluctuation of combinations, and this pushes up the production cost.
Furthermore, where the aligning member and the turntable are configured solely of metallic materials as in the conventional process, the usual shapes of the aligning member and the turntable do not permit fabrication by machining in only one direction, and the chucking directions of the aligning member and turntable under machining should be altered on the way, which would undeniably invite an increase in the number of machining steps. Moreover, the change in chucking direction makes it difficult to achieve coaxiality and therefore necessitates adjustment. Furthermore, in the small spindle motor for MD use which the prior art refers to, since both the aligning member 3 and the turntable 5 are very small and thin, their parts may be deformed by the heat in the cutting-off or lathing process, not only the machining time becomes a matter of concern but also dimensional measurement is required after completion. The aforementioned possibility of deformation reduces the yield. Obviously, steps of fastening the rotor yoke 9 and pressing the rotation shaft 8 in are necessitated.
Or if injection molding is used to reduce the production cost, it will be difficult to keep the precision of component parts equal to that of cutting of metallic materials, and this would adversely affect the alignment performance. Problems will also arise in the lubrication and durability of sliding portions.